PrepTest 112, Section 4, Question 19
Birds need so much food energy to maintain(69 more words not shown)
The argument relies on which(6 more words not shown)
- ABirds of different(13 more words not shown)
- BThe nectar-eating bird(6 more words not shown)
- CThe time it(30 more words not shown)
- DThe seed-eating bird(13 more words not shown)
- EThe overall energy(30 more words not shown)
Reading the argument
More energy in each mouthful doesn't tell us how long eating takes.
Suppose the two birds each need 500 calories. That number is just an illustration of their equal energy requirements. If nectar provides more energy for the same amount of food, the nectar-eating bird needs less food. But why must consuming that smaller amount take less time?
What if the nectar is sticky and slow to consume while the seeds are quick to eat? A sufficiently large difference in eating speed could outweigh the nectar's higher energy content. We aren't told that this is what happens. It's a possibility that exposes the missing comparison between food quantity and eating time.
What we’re looking for
The question asks for the questionable assumption. I'd look for something about how quickly the birds consume the same amount of food. The author has treated energy per amount as a guide to energy obtained per unit of time, and that move needs an assumption about eating speed.
Working the answers
- A
The argument chooses two birds with the same overall energy requirement. It doesn't need that to be typical of all pairs of species. Other birds could require very different amounts of energy while we still compare this pair. A's general claim doesn't address how quickly these birds eat.
- B
Occasionally eating seeds doesn't by itself settle the time comparison. The argument is about meeting equal energy needs through the two foods, and it doesn't require the nectar-eating bird to have an absolutely exclusive diet. A rare departure from its usual food wouldn't establish whether its usual feeding takes longer or less time.
- CCorrect
This supplies the assumed comparability in eating time: the nectar-eating bird doesn't take longer to consume the same amount of food. Together with nectar's greater energy content, that lets the author use the smaller amount needed as a reason to expect less time spent eating.
Without checking eating speed, the comparison could go badly. Nectar might take so much longer to consume that its energy advantage fails to save time. C rules out that timing disadvantage. The point is not that every tiny delay would erase the advantage, but that calorie density alone doesn't establish the claimed difference in eating time.
- D
The overall energy needs are already stipulated to be the same. Different body temperatures could coexist with that fact if other demands differed. We don't need matching temperatures to ask how long each bird takes to obtain the energy it needs. D supplies no eating-speed comparison.
- E
Many factors could affect a bird's energy needs. That doesn't prevent two birds from ending up with the same overall requirement, which is the case the author has chosen. Denying every influence of size, nest-building or climate is unnecessary. We need a link from the foods' energy content to consumption time, not a theory making all birds' requirements alike.
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